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320 lines
12 KiB
C++
320 lines
12 KiB
C++
//===-- Local.cpp - Functions to perform local transformations ------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file was developed by the LLVM research group and is distributed under
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// the University of Illinois Open Source License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This family of functions perform various local transformations to the
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// program.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/Constants.h"
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#include "llvm/DerivedTypes.h"
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#include "llvm/Instructions.h"
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#include "llvm/Intrinsics.h"
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#include "llvm/Analysis/ConstantFolding.h"
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#include "llvm/Support/GetElementPtrTypeIterator.h"
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#include "llvm/Support/MathExtras.h"
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#include <cerrno>
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#include <cmath>
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using namespace llvm;
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//===----------------------------------------------------------------------===//
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// Local constant propagation...
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//
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/// doConstantPropagation - If an instruction references constants, try to fold
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/// them together...
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///
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bool llvm::doConstantPropagation(BasicBlock::iterator &II) {
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if (Constant *C = ConstantFoldInstruction(II)) {
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// Replaces all of the uses of a variable with uses of the constant.
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II->replaceAllUsesWith(C);
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// Remove the instruction from the basic block...
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II = II->getParent()->getInstList().erase(II);
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return true;
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}
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return false;
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}
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/// ConstantFoldInstruction - Attempt to constant fold the specified
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/// instruction. If successful, the constant result is returned, if not, null
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/// is returned. Note that this function can only fail when attempting to fold
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/// instructions like loads and stores, which have no constant expression form.
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///
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Constant *llvm::ConstantFoldInstruction(Instruction *I) {
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if (PHINode *PN = dyn_cast<PHINode>(I)) {
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if (PN->getNumIncomingValues() == 0)
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return Constant::getNullValue(PN->getType());
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Constant *Result = dyn_cast<Constant>(PN->getIncomingValue(0));
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if (Result == 0) return 0;
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// Handle PHI nodes specially here...
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for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i)
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if (PN->getIncomingValue(i) != Result && PN->getIncomingValue(i) != PN)
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return 0; // Not all the same incoming constants...
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// If we reach here, all incoming values are the same constant.
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return Result;
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} else if (CallInst *CI = dyn_cast<CallInst>(I)) {
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if (Function *F = CI->getCalledFunction())
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if (canConstantFoldCallTo(F)) {
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std::vector<Constant*> Args;
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for (unsigned i = 1, e = CI->getNumOperands(); i != e; ++i)
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if (Constant *Op = dyn_cast<Constant>(CI->getOperand(i)))
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Args.push_back(Op);
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else
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return 0;
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return ConstantFoldCall(F, Args);
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}
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return 0;
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}
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Constant *Op0 = 0, *Op1 = 0;
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switch (I->getNumOperands()) {
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default:
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case 2:
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Op1 = dyn_cast<Constant>(I->getOperand(1));
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if (Op1 == 0) return 0; // Not a constant?, can't fold
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case 1:
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Op0 = dyn_cast<Constant>(I->getOperand(0));
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if (Op0 == 0) return 0; // Not a constant?, can't fold
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break;
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case 0: return 0;
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}
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if (isa<BinaryOperator>(I) || isa<ShiftInst>(I))
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return ConstantExpr::get(I->getOpcode(), Op0, Op1);
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switch (I->getOpcode()) {
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default: return 0;
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case Instruction::Cast:
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return ConstantExpr::getCast(Op0, I->getType());
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case Instruction::Select:
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if (Constant *Op2 = dyn_cast<Constant>(I->getOperand(2)))
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return ConstantExpr::getSelect(Op0, Op1, Op2);
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return 0;
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case Instruction::GetElementPtr:
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std::vector<Constant*> IdxList;
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IdxList.reserve(I->getNumOperands()-1);
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if (Op1) IdxList.push_back(Op1);
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for (unsigned i = 2, e = I->getNumOperands(); i != e; ++i)
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if (Constant *C = dyn_cast<Constant>(I->getOperand(i)))
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IdxList.push_back(C);
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else
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return 0; // Non-constant operand
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return ConstantExpr::getGetElementPtr(Op0, IdxList);
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}
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}
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// ConstantFoldTerminator - If a terminator instruction is predicated on a
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// constant value, convert it into an unconditional branch to the constant
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// destination.
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//
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bool llvm::ConstantFoldTerminator(BasicBlock *BB) {
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TerminatorInst *T = BB->getTerminator();
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// Branch - See if we are conditional jumping on constant
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if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
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if (BI->isUnconditional()) return false; // Can't optimize uncond branch
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BasicBlock *Dest1 = cast<BasicBlock>(BI->getOperand(0));
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BasicBlock *Dest2 = cast<BasicBlock>(BI->getOperand(1));
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if (ConstantBool *Cond = dyn_cast<ConstantBool>(BI->getCondition())) {
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// Are we branching on constant?
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// YES. Change to unconditional branch...
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BasicBlock *Destination = Cond->getValue() ? Dest1 : Dest2;
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BasicBlock *OldDest = Cond->getValue() ? Dest2 : Dest1;
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//cerr << "Function: " << T->getParent()->getParent()
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// << "\nRemoving branch from " << T->getParent()
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// << "\n\nTo: " << OldDest << endl;
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// Let the basic block know that we are letting go of it. Based on this,
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// it will adjust it's PHI nodes.
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assert(BI->getParent() && "Terminator not inserted in block!");
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OldDest->removePredecessor(BI->getParent());
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// Set the unconditional destination, and change the insn to be an
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// unconditional branch.
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BI->setUnconditionalDest(Destination);
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return true;
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} else if (Dest2 == Dest1) { // Conditional branch to same location?
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// This branch matches something like this:
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// br bool %cond, label %Dest, label %Dest
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// and changes it into: br label %Dest
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// Let the basic block know that we are letting go of one copy of it.
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assert(BI->getParent() && "Terminator not inserted in block!");
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Dest1->removePredecessor(BI->getParent());
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// Change a conditional branch to unconditional.
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BI->setUnconditionalDest(Dest1);
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return true;
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}
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} else if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) {
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// If we are switching on a constant, we can convert the switch into a
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// single branch instruction!
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ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition());
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BasicBlock *TheOnlyDest = SI->getSuccessor(0); // The default dest
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BasicBlock *DefaultDest = TheOnlyDest;
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assert(TheOnlyDest == SI->getDefaultDest() &&
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"Default destination is not successor #0?");
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// Figure out which case it goes to...
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for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) {
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// Found case matching a constant operand?
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if (SI->getSuccessorValue(i) == CI) {
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TheOnlyDest = SI->getSuccessor(i);
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break;
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}
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// Check to see if this branch is going to the same place as the default
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// dest. If so, eliminate it as an explicit compare.
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if (SI->getSuccessor(i) == DefaultDest) {
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// Remove this entry...
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DefaultDest->removePredecessor(SI->getParent());
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SI->removeCase(i);
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--i; --e; // Don't skip an entry...
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continue;
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}
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// Otherwise, check to see if the switch only branches to one destination.
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// We do this by reseting "TheOnlyDest" to null when we find two non-equal
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// destinations.
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if (SI->getSuccessor(i) != TheOnlyDest) TheOnlyDest = 0;
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}
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if (CI && !TheOnlyDest) {
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// Branching on a constant, but not any of the cases, go to the default
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// successor.
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TheOnlyDest = SI->getDefaultDest();
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}
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// If we found a single destination that we can fold the switch into, do so
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// now.
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if (TheOnlyDest) {
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// Insert the new branch..
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new BranchInst(TheOnlyDest, SI);
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BasicBlock *BB = SI->getParent();
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// Remove entries from PHI nodes which we no longer branch to...
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for (unsigned i = 0, e = SI->getNumSuccessors(); i != e; ++i) {
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// Found case matching a constant operand?
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BasicBlock *Succ = SI->getSuccessor(i);
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if (Succ == TheOnlyDest)
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TheOnlyDest = 0; // Don't modify the first branch to TheOnlyDest
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else
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Succ->removePredecessor(BB);
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}
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// Delete the old switch...
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BB->getInstList().erase(SI);
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return true;
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} else if (SI->getNumSuccessors() == 2) {
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// Otherwise, we can fold this switch into a conditional branch
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// instruction if it has only one non-default destination.
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Value *Cond = new SetCondInst(Instruction::SetEQ, SI->getCondition(),
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SI->getSuccessorValue(1), "cond", SI);
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// Insert the new branch...
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new BranchInst(SI->getSuccessor(1), SI->getSuccessor(0), Cond, SI);
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// Delete the old switch...
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SI->getParent()->getInstList().erase(SI);
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return true;
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}
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}
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return false;
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}
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/// ConstantFoldLoadThroughGEPConstantExpr - Given a constant and a
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/// getelementptr constantexpr, return the constant value being addressed by the
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/// constant expression, or null if something is funny and we can't decide.
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Constant *llvm::ConstantFoldLoadThroughGEPConstantExpr(Constant *C,
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ConstantExpr *CE) {
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if (CE->getOperand(1) != Constant::getNullValue(CE->getOperand(1)->getType()))
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return 0; // Do not allow stepping over the value!
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// Loop over all of the operands, tracking down which value we are
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// addressing...
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gep_type_iterator I = gep_type_begin(CE), E = gep_type_end(CE);
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for (++I; I != E; ++I)
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if (const StructType *STy = dyn_cast<StructType>(*I)) {
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ConstantUInt *CU = cast<ConstantUInt>(I.getOperand());
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assert(CU->getValue() < STy->getNumElements() &&
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"Struct index out of range!");
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unsigned El = (unsigned)CU->getValue();
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if (ConstantStruct *CS = dyn_cast<ConstantStruct>(C)) {
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C = CS->getOperand(El);
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} else if (isa<ConstantAggregateZero>(C)) {
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C = Constant::getNullValue(STy->getElementType(El));
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} else if (isa<UndefValue>(C)) {
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C = UndefValue::get(STy->getElementType(El));
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} else {
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return 0;
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}
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} else if (ConstantInt *CI = dyn_cast<ConstantInt>(I.getOperand())) {
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const ArrayType *ATy = cast<ArrayType>(*I);
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if ((uint64_t)CI->getRawValue() >= ATy->getNumElements()) return 0;
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if (ConstantArray *CA = dyn_cast<ConstantArray>(C))
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C = CA->getOperand((unsigned)CI->getRawValue());
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else if (isa<ConstantAggregateZero>(C))
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C = Constant::getNullValue(ATy->getElementType());
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else if (isa<UndefValue>(C))
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C = UndefValue::get(ATy->getElementType());
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else
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return 0;
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} else {
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return 0;
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}
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return C;
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}
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//===----------------------------------------------------------------------===//
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// Local dead code elimination...
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//
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bool llvm::isInstructionTriviallyDead(Instruction *I) {
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if (!I->use_empty() || isa<TerminatorInst>(I)) return false;
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if (!I->mayWriteToMemory()) return true;
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if (CallInst *CI = dyn_cast<CallInst>(I))
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if (Function *F = CI->getCalledFunction())
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switch (F->getIntrinsicID()) {
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default: break;
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case Intrinsic::returnaddress:
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case Intrinsic::frameaddress:
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case Intrinsic::isunordered:
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case Intrinsic::ctpop:
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case Intrinsic::ctlz:
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case Intrinsic::cttz:
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case Intrinsic::sqrt:
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return true; // These intrinsics have no side effects.
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}
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return false;
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}
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// dceInstruction - Inspect the instruction at *BBI and figure out if it's
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// [trivially] dead. If so, remove the instruction and update the iterator
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// to point to the instruction that immediately succeeded the original
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// instruction.
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//
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bool llvm::dceInstruction(BasicBlock::iterator &BBI) {
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// Look for un"used" definitions...
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if (isInstructionTriviallyDead(BBI)) {
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BBI = BBI->getParent()->getInstList().erase(BBI); // Bye bye
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return true;
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}
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return false;
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}
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